Today there exist a number of examples of message based services that are provided in accordance with certain standards in digital communication systems. Examples of such services are SMS (Short Message Service) and USSD (Unstructured Supplementary Service Data) in the digital radio communication network GSM. Similar message based services exists, or will exist, in other existing or future digital radio communication networks, such as GPRS, CDMA, D-AMPS (IS-136), PDC (Pacific Digital Cellular), W-CDMA (Wideband Code Division Multiple Access) and UMTS/IMT-2000.
These message based services of different digital radio communication networks are normally used for transferring text information to be presented on the display of a receiving mobile station, but also for transferring text or data to be interpreted by a receiving mobile station in different ways. Thus, these message based services are also being used as a basis for providing different new types of supplementary services.
An example of the use of a message based service for providing a new type of service is described in International Publication No. WO 97/08906, which is incorporated herein by reference. In WO 97/08906 it is disclosed how messages of a message based service, such as the SMS service of a GSM network, are used for transferring agents from a server to a mobile communication station. The server transmits an SMS message with an agent to a mobile subscriber upon receipt of an e-mail addressed to that subscriber. The agent agent includes coded information instructing the mobile subscriber, i.e., a mobile station or its connected computer, how to initiate a particular action with respect to the e-mail, such as retrieving the e-mail from the server in order to display it. Thus, a transferred SMS message and its agent is associated with an e-mail and is used to notify a user of a mobile communication station that an e-mail has been received. In addition to enable a mobile subscriber to read an e-mail, the service provides a number of other options for how the e-mail can be accessed, such as deleting it, forwarding it to a fax or another mobile subscriber etc.
SMTP (Simple Mail Transfer Protocol), POP3 (Post Office Protocol, version 3) and IMAP4 (Internet Message Access Protocol, version 4) are protocols for transfer and delivery of e-mails. Even though a person skilled in the art is well familiar with these protocols, some of their features and operations will be discussed below when further describing the technical background and problems with prior art with respect to the present invention.
The SMTP is a protocol which provides mechanisms for transmission of e-mails from a sending mail server host to a receiving mail server host. SMTP is independent of the particular transmission system and will transfer e-mails directly between two mail server hosts when the two hosts are connected to the same transport service, or via one or more relay SMTP servers when the sending and receiving hosts are not connected to the same transport service. The transmission includes routing, acceptance and delivery between the mail server host. Examples of transport services are TCP (Transmission Control Protocol) and X.25. At the sending SMTP server an SMTP sender process initiates a transport service connection to an SMTP receiver process at the receiving SMTP server. The SMTP sender process initiates SMTP commands and controls the transfer of an e-mail, the SMTP receiver process replies to the commands and performs the specified operations. If an end-user do not wish to have an SMTP server resident and continuously running on his computer, e.g., due to lack of computer resources or due to costs for being connected to a network, the user may choose to run a mail client program on his computer. In this case, an e-mail addressed to a specific mail box will be stored at a receiving mail server host before eventually being delivered to a mail client corresponding to the mail box.
POP3 is a protocol which allows for an e-mail to remain on a receiving mail server host until a mail client, i.e., a user, is ready to receive it. When the mail client is connected to the mail server host and requests a stored e-mail, the e-mail is downloaded from the user's mail box to the mail client. POP3 is a protocol typically used by Internet Service Providers to enable their end-users to access their e-mails. POP3 is a so called off-line protocol, which means that e-mails are downloaded from the mail server host, stored on the users local hard disk, deleted from the server host and then displayed to the user. Another e-mail delivery protocol is IMAP4. IMAP4 is an on-line protocol which means that a user not only is able to manage his e-mails off-line but also on-line, by enabling e-mails and folders to be permanently stored in a storage area of the server host. This resembles some of the existing proprietary e-mail systems and is useful if a user utilizes more than one computer for accessing his e-mails, e.g., a stationary computer at the office and a portable computer during travel, since the e-mails are stored on the server and can be accessed from whatever computer used.
The mail server to which a user connects with a POP3 mail client includes a POP3server host. When a user wishes to make use of the e-mail service he establishes a connection with the server host from the mail client and exchanges commands and responses with the POP3 server host during a session. Similarly, when the mail server host operates in accordance with the IMAP4 protocol, a mail client connects to the IMAP4 server host for exchanging commands and responses during a session.
The e-mails stored by a POP3 server host or a IMAP4 server host are accessed by the use of numbers. These numbers are either message sequence numbers or unique identifiers (UIDs). Unlike message sequence numbers, unique identifiers persist across sessions between the mail client and the mail server host. A unique identifier uniquely identifies an e-mail stored at the mail server host and consists of a server-determined string of one to 70 characters. The server should never reuse a unique identifier in a given mail box. The UIDs can be listed with a UIDL command which returns the UIDs for each e-mail in the mail box. Alternatively, the UIDL command is followed by a message sequence number, in which case the UID of the e-mail message, which during this specific session has the given message sequence number, is returned. Using a UID, a mail client can retrieve a specific corresponding message from the POP3 or IMAP4 server host independent of the specific session. With the IMAP4 protocol, additional operations can be preformed with respect to an e-mail using its corresponding UID.
Thus, if an end-user wishes to identify and retrieve a particular e-mail from a mail server host he has to list all the UIDs of the e-mails in the mail box. A specific e-mail can then be retrieved using the corresponding UID together with an appropriate command. If a POP3 or IMAP4 mail client is running on a mobile communication station and if a message based service were to be used for notifying a mobile subscriber of a new received e-mail, the mobile subscriber still have to list either the UIDs or the message sequence numbers of all e-mails in his mail box. The user would most likely not be able to ask the server host for the UID using the appropriate command together with a message sequence number argument, since it most often would not be possible for the user to know how many e-mails he had in his mail box when the current session with the server host started. The user can acquire the number of e-mail messages in the mail box by issuing an appropriate command. He would then receive a response after which a command together with the highest message sequence number could be issued for retrieving the UID of the last received e-mail.
Irrespective of which of the above-mentioned methods that are used for retrieving a specific e-mail, or for retrieving the last received e-mail, the communication between the mail server host and the mail client resulting from the commands issued, and/or listing of UIDs or message sequence numbers, will load down the mail system as well as the digital radio communication system, not to say that it will slow down the performance of the mail service.